Complex section or shape structures—i.e. structures with deep longitudinal grooves and, for example, an “H” or “X” section—have enhanced mechanical yield strength and rigidity properties. However, these structures cause the appearance of disturbances in an airflow. Effectively, if such a part is placed in an airflow, pressure fluctuations caused by the marked geometric variations in the surface of the part cause the appearance of vortexes forming a parasite drag. The interaction between such a turbulent flow and the solid surfaces of the part then generate an aerodynamic noise.
Aircraft wing flap systems and landing gear are therefore responsible, in the landing approach phase, for half of the noise perceived on the ground. Indeed, during this phase, the landing gear is lowered long before landing, for safety reasons, which causes the appearance of a highly turbulent flow and an aerodynamic noise.
Moreover, during approach and take-off phases, the aircraft requires an optimum lift/drag ratio to best negotiate the flying conditions, speed being particularly low in these phases. An optimum lift/drag ratio is obtained with minimal drag.
Furthermore, on take-off, an excess of drag requires an increase in thrust. Conversely, reducing drag makes it possible to optimise the thrust of the engine in this phase.
To reduce aerodynamic noise, the use of metal fairings, potentially articulated, to protect areas with complex-section parts to deflect airflows has been proposed, for example beneath the rocker arm of the landing gear, between the nose-gear actuating cylinders.
A sufficient number of these fairing parts must be securely fixed to comply with safety standards. These parts must also comply with constraints relating to retraction, hold space occupied when retracted, impact strength and aerodynamic loads, while limiting their mass load.
It is also possible to shape complex-shape parts by filling the grooves in order to create flat faces, without fairings. However, this solution may increase the mass of the landing gear. Moreover, if complex-section parts are replaced with bars, their mechanical properties can only be retained by increasing the size of the parts, and therefore the space they occupy.
Another solution involves applying a coating material with a lower density than that of the complex structural part in order to make its shape more aerodynamic without changing its mechanical properties. However, such an approach conflicts with maintenance conditions and complicates maintenance work. Indeed, such coatings require the removal of the structural part, prevent certain elements of the landing gear from being checked as the part is obscured, and need to be changed frequently on account of their usage conditions, resulting in additional grounding of the aircraft.